Method and apparatus for encoding/decoding images using a prediction method adopting in-loop filtering

ABSTRACT

Disclosed is a prediction method adopting in-loop filtering. According to the present invention, a prediction method for encoding and decoding video comprises the following steps: generating a residual block of the current block through an inverse quantization and inverse transform; generating a prediction block of the current block through an intra-prediction; performing in-loop filtering on the current block in which the residual block and the prediction block are combined; and storing the current block, on which the in-loop filtering is performed, in a frame buffer for an intra-prediction of the next block to be encoded. As described above, prediction is performed using an in-loop filter during processes for encoding and decoding video, thereby improving the accuracy of prediction and reducing errors in prediction, thus improving the efficiency of video compression and reducing the amount of data to be transmitted.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application Continuation application of application Ser. No.14/609,472, filed on Jan. 30, 2015, which is a continuation applicationof application Ser. No. 13/877,253, filed on Apr. 1, 2013, which is anational stage application of International Application No.PCT/KR2012/003125, filed on Apr. 23, 2012, which claims the benefit ofKorean Application No. 10-2011-0037484, filed on Apr. 21, 2011, theentire disclosures of which are incorporated herein by reference for allpurposes.

TECHNICAL FIELD

The present invention relates to video encoding and decoding, and moreparticularly, to a prediction method capable of reducing a predictionerror and increasing video compression efficiency by achieving moreaccurate prediction in a video encoding and decoding process.

BACKGROUND ART

A process of compressing video data to store or send the video data isrequired due to its large size. Typically, when video data is encoded,the video data is encoded by performing intra prediction or interprediction, transformation, quantization, entropy coding, or the like oneach picture of the video data in units of blocks.

Particularly, in the intra prediction, prediction from an adjacent blockis performed using spatial duplication in order to reduce duplication ofdata in a video. For example, in existing intra prediction of H.264/AVC,extrapolation is performed using nine modes. The intra prediction has adrawback in that accurate prediction is difficult as a pixel to bepredicted is away from a reference pixel. Particularly, use of existingintra prediction in representing texture degrades accuracy of theprediction.

Further, in the intra prediction or the inter-frame prediction,distortion between an original video and a restored video may occur ormay degrade accuracy of subsequent intra prediction or inter-frameprediction.

SUMMARY OF INVENTION Technical Problem

An object of the present invention for resolving the problems asdescribed above is to provide a prediction method capable of reducing aprediction error and reducing an amount of data to be sent from anencoder to a decoder by increasing prediction accuracy throughprediction with an in-loop filter.

Solution to Problem

The present invention for achieving the above object provides an intraprediction method for video encoding and decoding, the method includingsteps of: generating a residual block of a current block through inversequantization and inverse transformation; generating a prediction blockof the current block through intra prediction; performing in-loopfiltering on a current block obtained by summing the residual block andthe prediction block step; and storing the current block subjected tothe in-loop filtering in a frame buffer for intra prediction of a nextencoding target block.

Here, the step of generating a prediction block may include determiningan optimal prediction mode with minimum coding cost from pixels placedin an encoded or decoded block adjacent to the current block andgenerating a prediction block having a prediction pixel value predictedaccording to the determined prediction mode.

Here, the step of generating a prediction block may include forming atemplate for an encoded or decoded block adjacent to the current blockand generating a prediction block having a prediction pixel value frompixels of the template.

Here, the step of performing in-loop filtering may include performingthe in-loop filtering on a down boundary and right boundary of thecurrent block.

Here, the step of performing in-loop filtering may include adjustingwhether to perform filtering, the type of filtering, and intensity ofthe filtering based on an intra prediction direction of blocks adjacentto the current block.

Here, the step of performing in-loop filtering may include adjustingwhether to perform filtering, the type of filtering, and intensity ofthe filtering according to whether prediction methods for the currentblock and the block adjacent to the current block are the same or not.

An aspect of the present invention for achieving the other objectprovides a prediction method for video encoding and decoding, the methodincluding steps of: generating a residual video of a current videosubjected to inverse quantization and inverse transformation; generatinga prediction video of the current video through intra prediction orinter-frame prediction; summing the residual video and the predictionvideo to generate a restored video, and performing in-loop filtering onthe restored video based on distortion between an original video of therestored video and the restored video or based on characteristics of therestored video; and storing the restored video subjected to the in-loopfiltering in a frame buffer for prediction of a next encoding targetvideo.

Here, the step of performing in-loop filtering may include de-blockingfiltering, and may further include at least one additional filtering.

Here, the at least one additional filtering may include performingfiltering on the restored video using a difference between a pixel ofthe original video and a pixel of the restored video due to distortionbetween the original video of the restored video and the restored videoor using a coefficient based on the difference.

Here, the step of performing in-loop filtering may include determiningthe number of filterings or the type of filtering based on a size ordirectivity of a block into which the restored video has been dividedfor the in-loop filtering.

Another aspect of the present invention for achieving the other objectprovides a device for video encoding, the device including: a predictionunit that generates a prediction video of a current video through intraprediction or inter-frame prediction; a subtraction unit that generatesa residual video of a current video through inverse quantization andinverse transformation; an in-loop filter unit that sums the residualvideo and the prediction video to generate a restored video, andperforms in-loop filtering on the restored video based on distortionbetween an original video of the restored video and the restored videoor based on characteristics of the restored video; and a memory unitthat stores the restored video subjected to the in-loop filtering forprediction of a next encoding target video.

A still another aspect of the present invention for achieving the otherobject provides a device for video decoding, the device including: adecoding unit that generates a residual video of a current video bydecoding a bit stream; a prediction unit that generates a predictionvideo of a current video through intra prediction or inter-frameprediction; an addition unit that sums the residual video and theprediction video to generate a restored video; an in-loop filter unitthat performs in-loop filtering on the restored video based ondistortion between an original video of the restored video and therestored video or based on characteristics of the restored video; and amemory unit that stores the restored video subjected to the in-loopfiltering for prediction of a next encoding target video.

A still another aspect of the present invention for achieving the otherobject provides a method for video decoding, the method including stepsof: generating a residual video of a current video by decoding a bitstream; generating a prediction video of a current video through intraprediction or inter-frame prediction; summing the residual video and theprediction video to generate a restored video; performing in-loopfiltering on the restored video based on distortion between the originalvideo of the restored video and the restored video or based oncharacteristics of the restored video; and storing the restored videosubjected to the in-loop filtering for prediction of a next encodingtarget video.

Advantageous Effects of Invention

With the prediction method according to the present invention asdescribed above, it is possible to increase prediction accuracy, reducea prediction error, increase video compression efficiency, and reduce anamount of data to be sent by performing prediction with the in-loopfilter in the video encoding and decoding process.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a flowchart for explaining an intra prediction methodaccording to the present invention.

FIG. 2 is a conceptual diagram for explaining intra prediction modes fora 4×4 pixel block in H.264/AVC.

FIG. 3A is a conceptual diagram for explaining an intra predictionmethod through formation of a template, and FIG. 3B is a conceptualdiagram for explaining a method of performing intra prediction from apreviously encoded region rather than an adjacent block.

FIG. 4 is a conceptual diagram for explaining various schemes of forminga template in an intra prediction method through template formation.

FIG. 5 is a conceptual diagram for explaining an example of in-loopfiltering in the intra prediction method according to the presentinvention.

FIGS. 6A and 6B are conceptual diagrams for explaining a concept ofin-loop filtering for a current block boundary in the intra predictionmethod according to the present invention.

FIGS. 7A and 7B are conceptual diagrams for explaining a concept ofperforming in-loop filtering based on a prediction mode of a blockadjacent to a current block.

FIG. 8 is a conceptual diagram for explaining a concept of adjustingpresence or absence and intensity of in-loop filtering in the predictionmethod according to the present invention.

FIG. 9 is a conceptual diagram for explaining a concept of formingdifference information of a motion vector and a predictor.

FIG. 10 is a block diagram for explaining a configuration example of avideo encoding device in which the intra prediction method according tothe present invention has been implemented.

FIG. 11 is a block diagram for explaining a configuration example of avideo decoding device in which the intra prediction method according tothe present invention has been implemented.

FIG. 12 is a conceptual diagram illustrating a video encoding methodaccording to an embodiment of the present invention.

DESCRIPTION OF EMBODIMENTS

While the present invention is susceptible to various modifications andmay have several embodiments, specific embodiments thereof are shown byway of example in the drawings and will herein be described in detail.It should be understood, however, that there is no intent to limit theinvention to the particular forms, but on the contrary, the invention isto cover all modifications, equivalents, and alternatives falling withinthe spirit and scope of the invention. Like numbers refer to likeelements throughout the description of the figures.

It will be understood that, although the terms first, second, A, B, etc.may be used herein to describe various elements, these elements shouldnot be limited by these terms. These terms are only used to distinguishone element from another. For example, a first element could be termed asecond element, and, similarly, a second element could be termed a firstelement, without departing from the scope of the present invention. Asused herein, the term “and/or” includes any and all combinations of oneor more of the associated listed items.

It will be understood that when an element is referred to as being“connected” or “coupled” to another element, it can be directlyconnected or coupled to the other element or intervening elements may bepresent. On the other hand, it will be understood that when an elementis referred to as being “directly connected” or “directly coupled” toanother element, there are no intervening elements present.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”,“comprising,”, “includes” and/or “including”, when used herein, specifythe presence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this invention belongs. It will befurther understood that terms, such as those defined in commonly useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art andwill not be interpreted in an idealized or overly formal sense unlessexpressly so defined herein.

Hereinafter, a video encoding device or a video decoding device thatwill be described below may refer to a user terminal such as a personalComputer (PC), a laptop computer, a personal digital assistant (PDA), aportable multimedia player (PMP), a play station portable (PSP), awireless communication terminal, a smart phone, or a TV, or a serverterminal such as an application server or a service server, or mayrefers to any device including a communication device such as acommunication modem for performing communication with various devices ora wired/wireless communication network, a memory for storing variousprogram and data for coding or decoding a video or performinginter-frame or intra prediction for coding or decoding, a microprocessorfor executing the program to perform computation and control, and thelike.

Further, a video encoded into a bit stream by the video encoding devicemay be sent to the video decoding device in real time or in non-realtime via a wired/wireless communication network such as the Internet, awireless local area communication network, a wireless LAN network, aWibro network, or a mobile communication network or via variouscommunication interfaces such as cable or universal serial bus (USB),and decoded by the video decoding device to be restored and played backas a video.

Typically, a video may include a series of pictures, and each picturemay be divided into a predetermined region such as a frame or block.When a region of the video is divided into blocks, the divided block maybe greatly classified into an intra block and an inter block accordingto a coding method. The intra block refers to a block encoded using anintra prediction coding scheme. The intra prediction coding refers to ascheme of generating a prediction block by predicting a pixel of acurrent block using pixels of previously encoded, decoded and restoredblocks in a current picture that is currently encoded, and encoding adifference value between the prediction block and the current block. Theinter block refers to a block encoded using inter prediction coding. Theinter prediction coding refers to a scheme of generating a predictionblock by predicting a current block in a current picture by referencingone or more past or future pictures, and encoding a difference valuebetween the prediction block and the current block. Here, a framereferenced to encode or decode the current picture is referred to as areference frame.

Hereinafter, a preferred embodiment according to the present inventionwill be described in detail with reference to the accompanying drawings.

Meanwhile, the following embodiments will be described based onH.264/AVC codec in order to confirm performance of the presentinvention, but the technical spirit of the present invention may bewidely applied to H.264/AVC as well as video compression technology withan intra prediction method.

Overview of Intra Prediction Method According to the Present Invention

FIG. 1 is a flowchart for explaining an intra prediction methodaccording to the present invention.

Referring to FIG. 1, an intra prediction method according to the presentinvention may include step S110 of generating a residual block throughinverse quantization and inverse transformation, step S120 of generatinga prediction block through intra prediction, step S130 of performingin-loop filtering on a current block obtained by summing the residualblock and the prediction block, and step S140 of storing the currentblock subjected to the in-loop filtering in a frame buffer for intraprediction of a next encoding target block, in an intra predictionmethod.

First, step S110 is a step of generating a residual block throughinverse quantization and inverse transformation, and may be describeddifferently according to a case in which the intra prediction isperformed in a video coding process and a case in which the intraprediction is performed in a video decoding process.

When step S110 described above is performed in the video coding process,a residual block having a difference value between a predictedprediction block and a encoding target block is subjected totransformation and quantization and then to inverse quantization andinverse transformation. This is a process for re-generating, in thecoding process, the same residual block as a residual block generatedthrough inverse quantization and inverse transformation in a decodingprocess, and referencing the residual block in a subsequent codingprocess. That is, the residual block generated herein is a block summedwith the intra-predicted prediction block to generate a current block inthe video coding process.

When step S110 described above is performed in the video decodingprocess, a residual block is generated through entropy decoding, inversequantization and inverse transformation from a received bit stream. Thatis, the residual block generated in the video coding process describedabove and the residual block generated in the video decoding processhave the same configuration. In this case, in the inverse quantizationprocess, quantization frequency coefficients of the quantized residualblock are inversely quantized to generate a frequency coefficient, andin the inverse transformation process, the residual block inverselyquantized through the inverse quantization is inversely transformed.

Next, step S120 is a step of generating a prediction block through theintra prediction. Two representative methods below may be used.

In a first method, a pixel value of each pixel in a current block to beencoded in a video is predicted from pixels in an adjacent blockaccording to an optimal determined prediction mode, and a predictionblock having the prediction pixel value of each pixel is generated.Here, as the optimal prediction mode, a prediction mode with minimumcoding cost may be determined from among various intra prediction modesfor intra prediction (e.g., in H.264/AVC, nine prediction modes in eachof intra 8×8 prediction and intra 4×4 prediction and four predictionmodes in intra 16×16 prediction).

FIG. 2 is a conceptual diagram for explaining intra prediction modes fora 4×4 pixel block in H.264/AVC.

Referring to FIG. 2, intra prediction modes of a 4×4 pixel block includenine prediction modes, including a vertical mode 210, a horizontal mode220, a DC (Direct Current) mode 230, a diagonal down-left mode 240, adiagonal down-right mode 250, a vertical-right mode 260, ahorizontal-down mode 270, a vertical-left mode 280 and a horizontal-upmode 290. Meanwhile, In the case of a 16×16 pixel block, there are fourprediction modes. In HEVC, more prediction modes are prepared. In stepS120 of generating a prediction block, coding cost of each predictionmode may be calculated according to a block mode or a block size of aencoding target block, and a prediction mode with minimum coding costmay be determined as an optimal intra prediction mode to generate theprediction block.

As a second method, the prediction block generation step S120 describedabove may be performed using another method discussed in HEVC(High-Efficiency Video Coding) or the like that is standardized as anext-generation video compression standard of H.264/AVC, and greatly,two schemes are available. However, the prediction block generation stepS120 may be performed using two methods that will be described below aswell as various prediction methods for generating a prediction blockfrom a previously encoded region.

FIG. 3A is a conceptual diagram for explaining an intra predictionmethod through formation of a template, and FIG. 3B is a conceptualdiagram for explaining a method of performing intra prediction from apreviously encoded region rather than an adjacent block.

Referring to FIG. 3A, in the prediction block generation step S120, atemplate 311 for a current block 310 to be encoded in a video may beformed, and a previously encoded region of a current picture may besearched for a candidate template 321 most similar to the formedtemplate to predict the current block from a candidate block 320 inwhich a pixel value of each pixel has been previously encoded or decodedin a frame.

Further, in the prediction block generation step S120, as shown in FIG.3B, a previously encoded search region 340 of a current picture may besearched for a candidate block 350 most similar to the current block 330to generate a prediction block, as in inter-frame prediction. In thiscase, when the previously encoded region of the current picture issearched for the block most similar to the current block to generate theprediction block as in the inter-frame prediction, information for amotion vector or the like may be sent to a decoder.

When the block is predicted through extrapolation in the first method,it is difficult to accurately predict the block if the block is awayfrom the referenced adjacent block or if the current block is includedin a repeated region. This problem can be overcome by the method ofFIGS. 3A and 3B described above.

FIG. 4 is a conceptual diagram for explaining various schemes of forminga template in an intra prediction method through template formation.

Referring to FIG. 4 together with FIG. 3A, when a current block ispredicted using the template, the template may be formed by differentlysetting a, b, m, and n or may be set to have various shapes.

In this case, the same fixed values of a, b, m, and n of the templatemay be used in the encoder and the decoder, and information on the shapeof the template may be sent to the decoder. In this case, the sentinformation may be sent in units of pictures, slices, blocks, sub-blocksor the like.

Next, step S130 is a step of performing in-loop filtering on a currentblock obtained by summing the residual block and the prediction block.That is, in the in-loop filtering step S130, a restored current block isfiltered. In this case, the filtering is performed to reduce aquantization error or a screen burn-in phenomenon between blocks. When,in the prediction block generation step S120, the prediction isperformed by using the template or by searching for the block mostsimilar to the current block, as in the inter-frame prediction, in theintra prediction method, burn-in may exist between blocks or aquantization error may be large in the previously encoded region. Inthis case, when a template most similar to the template from theadjacent block and the template in the previously encoded region, thesimilar template cannot be searched for or when a block most similar tothe current block is searched for, the similar template cannot besearched for. Accordingly, the in-loop filtering is applied when codingends in units of blocks.

In this case, the filtering may be performed using an existingde-blocking filter or a scheme similar to or different from thede-blocking filter. The de-blocking filter softens a boundary betweenthe blocks to improve image quality of an encoded or decoded frame.

Further, in the embodiment of the present invention, a filter of anotherscheme for improving the image quality of the encoded or decoded framemay be applied. A distortion between an original video and a restoredvideo occurring through a coding process, such as quantization, can becompensated through a filter using a difference between a pixel of theoriginal video and a pixel of the restored video due to the distortionor using a coefficient based on the difference. That is, a referencevideo can be created using a filter capable of compensating for thedistortion between the original video and the restored video, and codingefficiency can be improved through the reference video. Further, it ispossible to increase accuracy of subsequent intra prediction orinter-frame prediction by reducing the distortion by performingfiltering based on characteristics of the restored video and improvecoding efficiency.

Lastly, in step S140, the current block subjected to the in-loopfiltering is stored in a frame buffer memory for intra prediction of anext encoding target block.

The intra prediction method according to the present invention describedabove may be more readily described through a configuration of a videoencoding device and a video decoding device in which the intraprediction method has been actually implemented, which will be describedbelow. Hereinafter, some embodiments of the intra prediction methodaccording to the present invention described above will be described indetail. A first embodiment and a second embodiment are embodiments inwhich the in-loop filtering step S130 of the intra prediction methodaccording to the present invention is further embodied. A thirdembodiment is an embodiment in which the prediction block generationstep S120 of the intra prediction method according to the presentinvention is further embodied. A fourth embodiment and a fifthembodiment are embodiments in which a method of reducing an amount ofinformation delivered from the encoder to the decoder is provided whenthe intra prediction method according to the present invention isapplied.

First Embodiment of Intra Prediction Method According to the PresentInvention

FIG. 5 is a conceptual diagram for explaining an example of in-loopfiltering in the intra prediction method according to the presentinvention. FIG. 6 is a conceptual diagram for explaining a concept ofin-loop filtering for a current block boundary in the intra predictionmethod according to the present invention.

Referring to FIG. 5, in the intra prediction method according to thepresent invention, in-loop filtering is performed on the encoded currentblock 510.

In this case, when intra prediction is performed using the first methoddescribed above in the prediction block generation step S120, filteringis applied in a block prediction mode direction to reduce a quantizationerror. That is, referring to FIG. 6A, since a correlation betweendecoded pixels placed in the prediction direction is high, filtering isperformed on pixels placed at down and right block boundaries 511 and512 of the encoded block in the prediction mode direction to reduce thequantization error. Accordingly, when a block encoded or decodedsubsequent to the current block is predicted using the prediction blockgeneration method described with reference to FIG. 2, coding isperformed using a value similar to an original pixel value, therebyreducing the prediction error and increasing the coding efficiency.

Referring to FIG. 6B, the filtering is performed on the pixels placed atthe down and right block boundaries of the current block to reduce thequantization error, thereby reducing a prediction error of the blockencoded or decoded after the current block and increasing the codingefficiency.

Further, it is possible to reduce the prediction error by correcting thedifference between the original pixel and the restored pixel. In otherwords, filtering may be performed on the restored video or thedifference between the original pixel and the restored pixel may becorrected.

For example, a filtering coefficient value may be calculated based onthe difference between the original pixel and the restored pixel or acertain coefficient value may be predefined and used. Alternatively, thefiltering coefficient value may be calculated based on restored pixels.

When filter coefficient values are determined based on the differencebetween the original pixel and the restored pixel, information on thecoefficient value is sent to the decoder. This information may be sentin units of sequences, slices, blocks or the like. Further, when thecertain coefficient value is predefined and used or the filtercoefficient value is determined based on the restored pixels, theinformation may not be separately sent under promise between the encoderand the decoder. That is, it is possible to increase the predictionefficiency by filtering the pixels placed at the right and down blockboundaries of the block or all pixels in the block to reduce thequantization error. Alternatively, it is possible to reduce thequantization error by applying filtering for correcting a differencebetween the original pixel and the restored pixel based on thedifference, to the pixels placed at the down and right block boundariesof the current block or all the pixels in the block. In this case,information on the difference is sent to the decoder so that the sameprocess can be performed in the encoder and the decoder.

For example, when the intra prediction is performed using anextrapolation method, the restored block has a large influence onprediction accuracy for a next block to be encoded or decoded (a right,down or lower right block). Accordingly, when such a process isperformed, the prediction accuracy increases and the coding efficiencycan increase. For the information on the difference between the originalpixel and the restored pixel, a difference value may be sent in units ofpixels or pixels may be grouped according to a specific criterion and arepresentative difference value of each group may be sent to thedecoder. Here, the specific criterion may be a brightness value of thepixel, slope information or the like.

According to an embodiment of the present invention, a filter correctingthe difference value between the pixel of the original video and thepixel of the restored video due to the distortion between the originalvideo and the restored video may be corrected as in FIGS. 6A and 6B orusing a coefficient based on the difference may be applied.

In this case, information on the difference between the pixel of theoriginal video and the pixel of the restored video or the coefficientbased on the difference may be sent to the decoder in units ofsequences, pictures, slices, blocks or the like. Here, the correction ofthe difference between the original pixel and the restored pixel may beperformed by the filter. For example, when filtering is performed basedon the distortion between the original video and the restored video, theinformation on the difference between the pixel of the original videoand the pixel of the restored video may be sent to the decoder.

Accordingly, in coding or decoding according to an embodiment of thepresent invention, whether to perform filtering, the number of filtering(the type of filtering), a filtering direction and a filtering intensitymay be changed based on the distortion between the original video of therestored video and the restored video or based on characteristics of therestored video.

That is, according to an embodiment of the present invention, additionalfiltering for improving image quality of an encoded or decoded frame maybe applied. For additional filtering, a method using existingde-blocking filtering, as well as a method using the difference betweenthe pixel of the original video and the pixel of the restored video dueto distortion between the original video and the restored video or usingthe coefficient based on the difference may be utilized. Accordingly,the additional filtering may be applied independently from or togetherwith the de-blocking filtering. Whether to apply the additionalfiltering may be determined according to a size of the block ordirectivity of the block.

For example, at least one additional filtering described above may beselectively or essentially performed after the de-blocking filtering isperformed, and the number of filterings or the type of filtering may bedetermined according to the size or the directivity of the block inwhich the restored video is divided, for in-loop filtering.

Thus, it is possible to reduce the distortion between the original videoand the restored video and improve coding efficiency and subjectiveimage quality.

Second Embodiment of Intra Prediction Method According to the PresentInvention

FIG. 8 is a conceptual diagram for explaining a concept of adjustingpresence or absence and intensity of in-loop filtering in the predictionmethod according to the present invention.

In an existing in-loop filtering process, after the frame is coded, theframe is subjected to de-blocking filtering and stored in a memory. Wheninter-frame prediction is performed in a next frame, the framepreviously subjected to an in-loop filtering process is referenced.However, in the in-loop filtering proposed in the above invention,in-loop filtering is applied directly after one block is coded. Thisprocess is performed on a next block. Using this scheme, a block inwhich block burn-in has been removed can be predicted by referencing ablock in which the quantization error has been removed when thepreviously encoded block is referenced in a current frame in the intraprediction, which enables more excellent prediction. Further, even inthe prediction block generation method described with reference to FIGS.3A and 3B, since the block burn-in has been reduced at a block boundaryin the previously encoded region, the current block can be predictedwith high accuracy.

Meanwhile, whether to perform filtering, the number of filterings (thetype of filtering), filtering direction, and filtering intensity may bechanged according to a prediction mode of a block adjacent to thecurrent block.

FIGS. 7A and 7B are conceptual diagrams for explaining a concept ofperforming in-loop filtering based on a prediction mode of a blockadjacent to a current block.

Referring to FIG. 7A, a case in which prediction mode directions of acurrent block 710 and an adjacent block 720 are the same or similar isillustrated. In this case, filtering is performed on pixels placed inthe direction.

On the other hand, referring to FIG. 7B, since there is no continuitybetween a current block 730 and an adjacent block 740, weak filtering isperformed or no filtering is performed. If prediction modes of therespective blocks placed at both sides differ, the filtering isperformed using an existing method without considering the predictionmode direction. The different number of pixels may be applied thefiltering according to a size of the block.

In H.264 that is one existing coding method, there is de-blockingfiltering that plays a similar role to filtering that is performed onleft and up blocks encoded in the in-loop filtering step S130 of thepresent invention. In this de-blocking filtering process, when there arecoefficients to be sent in the inter-frame prediction, block burn-in isdetermined to be severe at a boundary of this portion and strongfiltering is performed. On the other hand, when there are nocoefficients to be sent, there is no or less quantization error in thisportion, due to absence of coefficients to be sent. Accordingly, weakfiltering is performed or no filtering is performed. Referring to FIG.8, in the prediction block generation step S120 of the intra predictionmethod according to the present invention, the encoded or decoded blocksas described with reference to FIG. 3B are searched for a block similarto the current block. When the scheme of generating the block searchedfor in this process as a prediction block for the current block is used,filtering is performed at left and up block boundaries after the blockcoding ends in the in-loop filtering S130. In this case, even in theintra prediction, when there are no coefficients to be sent, blockburn-in may be determined to be less than when there are coefficients tobe sent and weak filtering may be performed or no filtering may beperformed, as in the inter-frame prediction. This algorithm is appliedeven to the intra prediction used in FIG. 3A.

Further, in both the blocks, different filtering may be performedaccording to whether prediction of each block has been performed usingthe first method described with reference to FIG. 3A or the secondmethod described with reference to FIG. 3B. For example, when theprediction mode of both the blocks is performed using the second methodof the intra prediction, weak filtering may be performed (S850). This isbecause, when the prediction is performed using the second method, thepreviously encoded region of the current picture is searched for theblock similar to the current block and the prediction is performed, andaccordingly, a quantization error is determined to be less as inexisting inter-frame prediction, as shown in FIG. 8. Thus, weakerfiltering is performed as compared to the intra prediction.

Third Embodiment of Intra Prediction Method According to the PresentInvention

Meanwhile, in the prediction block generation step S120 of the intraprediction method according to the present invention, when a predictionmethod of forming a template for pixels of blocks adjacent to a currentblock to form a prediction block or searching a previously encodedregion for a block similar to the current block to generate the similarblock as a prediction block as described with reference to FIGS. 3A and3B is applied, the template may be formed or the similar block may besearched for with expansion up to a decimal fraction unit pixel ratherthan an integer unit.

That is, when the template is formed from an adjacent block and apreviously encoded region of a current picture is searched for a mostsimilar template to the template or the previously encoded region of thecurrent picture is searched for the block most similar to the currentblock to generate a prediction block, there is an advantage in that amore accurate block can be searched for when the prediction is performedwith expansion up to the decimal fraction unit.

In this case, for information indicating whether to form the template orsearching for the prediction block in integer units or with expansion upto any decimal fraction unit (½, ¼ or the like), the same fixed unit maybe used in the encoder and the decoder. When data is sent to determinethe unit, sending may be performed in several units such as pictures,slices, blocks, or sub-blocks. The above information may be sent or maynot be sent according to a prediction method used in the predictionblock generation step S120. When the prediction block is searched forwith the expansion up to the decimal fraction unit, severalinterpolation filters (e.g., a 6-tap FIR interpolation filter applied to¼ pixel inter-frame prediction of H.264/AVC) may be applied in order tocreate a pixel in a decimal fraction unit.

Fourth Embodiment of Intra Prediction Method According to the PresentInvention

The present embodiment illustrates an embodied configuration forreducing an amount of information delivered between the encoder and thedecoder when the scheme of searching a previously encoded region for thesimilar block to generate a prediction block has been applied, which hasbeen described with reference to FIG. 3B, in the prediction blockgeneration step S120 of the intra prediction method according to thepresent invention.

That is, in the prediction block generation step S120, when thepreviously encoded region of the current picture is searched for theblock most similar to the current block and prediction is performed, apredictor may be variously set and formed when information on a motionis to be sent.

For example, a coordinate at the upper left corner of the current blockmay be set as the predictor and information on a difference with amotion vector relative to the coordinate may be sent from the encoder tothe decoder. Alternatively, a coordinate determined by an optimaltemplate using the template may be set as the predictor, and theinformation on the difference with the motion vector may be sent to thedecoder with reference to the coordinate.

The encoder and the decoder may use the same fixed information, asinformation on the type of used predictor, and the information may besent in several cases such as a picture, a slice, a block, or asub-block. Additionally, several candidate groups of predictors areprepared (for example, several candidate groups including a coordinatein the upper left corner of the current block, and the coordinatedetermined by the optimal template using the template) and informationon optimal predictor candidates with low coding cost in the groups maybe sent.

For example, as in FIG. 4, when templates a, b and c are assumed to bepresent, a previously encoded region is searched for respective mostsimilar templates using the templates and the most similar templates areused as the predictors. In this case, information on shapes of thetemplates used as the predictors should be sent. Since the three currenttemplate predictors are used, a, b, and c may be indexed by 0, 10, and11 and the information may be set to the decoder. If a differencebetween values of (x, y) position coordinates of the optimal templatesis equal to or smaller than a threshold, the information on templatepredictor candidates may be omitted. If it is assumed that an optimaltemplate position of the first template predictor candidate among thethree template predictor candidates is (−7, −5) relative to a coordinatein the upper left corner of the current block, an optimal templateposition of the second template predictor candidate is (−6, −6), anoptimal template position of the third template predictor candidate (−7,−6) and the threshold is 2, the three optimal coordinates are in a rangeof the threshold. Accordingly, the templates are templates havingsimilar performance, the information on the optimal templates is notsent, and one of the three templates is used as the predictor accordingto a predefined rule.

If optimal searched template positions of two of the template predictorcandidates has a difference equal to or smaller than the threshold andthe optimal template predictor position of the other template predictorcandidate has a difference with the two optimal template predictorpositions greater than the threshold, the two template predictorcandidates are assumed to be templates having similar performance. Acomparison with the other template predictor candidate in a differencevalue with actual motion information is performed and information on thetemplate predictor candidate with less data is sent. (For example, whenthe optimal template position of the first template predictor is (−7,−5), the optimal template position of the second template predictor is(−6, −5), the optimal template position of the third template predictoris (−3, −1) and the threshold is 2, the first and second templatepredictors are grouped into one since optimal template positions of thefirst and second template predictors are in a range of the threshold,the optimal template position of the third template predictor is not inthe threshold range relative to the two optimal template positions ofthe first and second template predictors and accordingly, the thirdtemplate predictor becomes a different template. Accordingly, the numberof the template predictor candidates is 2 (the group is regarded as onetemplate). Codewords ‘0’ and ‘1’ may be allocated to the respectivetemplate predictor candidates and information on the template predictorcandidates may be set.)

Information on a difference between the motion vector and the predictormay include an absolute value of the difference and a sign component.

FIG. 9 is a conceptual diagram for explaining a concept of formingdifference information of a motion vector and a predictor.

Referring to FIG. 9, if the predictor is the same as a coordinate in theupper left corner of the current block described above when a positionof the current block 930 is the same as that illustrated in FIG. 9,information on a sign in a y-axis direction of the motion vector forspecifying a candidate block 940 is not necessary when the informationon the difference is sent to the decoder. Accordingly, sending theinformation on a sign to the decoder may be unnecessary (i.e., when thesign in the y-axis direction is fixed since the current block is locatedin a bottom edge of a search area). When the information on a sign isunnecessary according to the position of the predictor as in the abovecase, the information on the difference containing no information on asign is sent to the decoder, thereby increasing the efficiency.

Fifth Embodiment of Intra Prediction Method According to the PresentInvention

The present embodiment illustrates an embodied configuration forreducing an amount of information delivered between the encoder and thedecoder when the scheme of generating a prediction block using atemplate, which has been described with reference to FIG. 3A, is appliedin the prediction block generation step S120 of the intra predictionmethod according to the present invention.

That is, when the prediction block is generated using the template inthe prediction block generation step S120, several candidate templatesare formed and an optimal template is searched for. For example, inorder to search for a more accurate template, several candidatetemplates are formed and an optimal template is searched for, asdescribed with reference to FIG. 4.

Several templates, such as a template with high correlation in a regionon the left side of the current block as in FIG. 4a , a template havinga higher correlation in a region on the upper left side of the currentblock as in FIG. 4b , a template with high correlation in an entireposition of the current block as in FIG. 4c , and a template having ahigher correlation in a region on the upper side of the current block asin FIG. 4d , are formed to perform prediction. For example, when thethree templates shown in FIG. 4a, b, and c are candidates, an optimalprediction block is searched for with each template. Information for atemplate candidate with low coding cost among the three templatecandidates may be set and coding may be performed. The information ontemplate candidates is sent to the decoder because, although a templatewith lowest coding cost is recognized by the decoder using severaltemplate candidates, such a template may not be optimal. Thus,information for a template candidate with actually least coding costamong the several candidates is sent. In this case, a short codeword(e.g., ‘0’) may be allocated to a template candidate with a highestfrequency (or regarded as having a highest frequency), a long codeword(e.g., ‘10’ or ‘11’) may be allocated to other template candidates, andthen information on the template candidate may be sent. The allocationof the codeword to each candidate may be performed using severalmethods.

If differences of values of (x, y) coordinates of the optimal templatepositions searched for by the three template candidates are all equal toor smaller than a threshold, the information on a template candidate maybe omitted. (For example, if it is assumed that an optimal templateposition of the first template candidate is (−7, −5) with reference to acoordinate in the upper left corner of the current block, an optimaltemplate position of the second template candidate is (−6, −6), anoptimal template position of the third template candidate is (−7, −6),and the threshold is 2, the optimal coordinates of the three templatecandidates are in a range of the threshold. Accordingly, the templatecandidates are assumed to be templates having similar performance andthe information on the optimal templates is not sent and the currentblock is predicted using one of the three templates.)

If the optimal template positions searched for by two of the templatecandidates have a difference equal to or smaller than the threshold andthe optimal template position of the other template candidate has adifference with the two optimal template positions greater than thethreshold, the two template candidates are assumed to be templateshaving similar performance. A comparison with the other templatecandidate in coding cost is performed and information for the templatecandidate with low cost is sent. (For example, when the optimal templateposition of the first template is (−7, −5), the optimal templateposition of the second template is (−6, −5), the optimal templateposition of the third template is (−3, −1), and the threshold is 2, theoptimal template positions of the first and second templates is in arange of the threshold and accordingly, the first and second templatesare grouped into one. Since the third template is not in the thresholdrange relative to the two templates, the third template is a differenttemplate. Accordingly, the number of template candidates is 2 (the groupof the two templates is regarded as one template). Codewords ‘0’ and ‘1’may be allocated to the respective template candidates and theinformation on the template candidate may be sent.

Sixth Embodiment of Intra Prediction Method According to the PresentInvention

FIG. 12 is a conceptual diagram illustrating another embodiment of anintra prediction method according to the present invention.

The intra prediction method according to the present invention describedwith reference to FIG. 12 is a method of calculating a selectionprobability for an intra prediction method for a current block, which isan intra prediction target, according to a combination of intraprediction methods applied to blocks around the current block, andutilizing the probability in coding.

That is, it is a method of making coding in an intra prediction methodfor the current block efficient based on a probability inferred fromintra prediction methods applied to previously encoded blocks in anintra prediction coding process.

Referring to FIG. 12, when application of a first intra predictionmethod to a left block X or an up block Y of the current block isindicated by 0 and application of a second intra prediction method isindicated by 1, there are four combinations (0, 0), (1, 0), (0, 1), and(1, 1). For example, a case in which the first intra prediction methodis applied to both of the left block and the up block may be representedas (0, 0), and a case in which the first intra prediction method isapplied to the left block and the second intra prediction method isapplied to the up block may be represented as (0, 1).

In this case, the intra prediction method may refer to an intra modeprediction method based on extrapolation applied to H.264/AVC or thelike or the template matching method described above. That is, if thefirst intra prediction method indicated by 0 is the intra modeprediction method, the second intra prediction method indicated by 1 maybe the template matching prediction method.

Further, a probability of the first intra prediction method for thecurrent block being selected may be represented as a, and a probabilityof the second intra prediction method being selected may be representedas b. In this case, the intra prediction starts with predeterminedinitial values of a and b, and the values of a and b may be continuouslyupdated during intra prediction coding for blocks. Accordingly, theprobability a or b of the first intra prediction method or the secondintra prediction method being selected as the intra prediction method tobe applied to the current block may be selected according to acombination of the intra prediction methods applied to the left blockand the up block.

For example, in FIG. 12, when the first intra prediction method isapplied to both of the left block X and the up block Y, the probabilityto select the first intra prediction method for the current block ishigher. Accordingly, a higher probability is set for the first intraprediction method and coding is performed. This probability is appliedto a context-based arithmetic encoding scheme to improve efficiency ofentire coding.

Meanwhile, in the above-described embodiment, two selectable intraprediction methods are assumed. However, the same scheme may be appliedto a case in which there are three selectable intra prediction methods.A description of this case is the same as the foregoing descriptionexcept that the number of combinations of intra prediction methodsapplied to the left block and the up block increases.

Configuration Example of Video Encoding Device in which Intra PredictionMethod According to the Present Invention has been Implemented

Hereinafter, a configuration of a video encoding device in which theintra prediction method according to the present invention describedabove is implemented will be described.

FIG. 10 is a block diagram for explaining a configuration example of avideo encoding device in which the intra prediction method according tothe present invention has been implemented.

Referring to FIG. 10, a video encoding device may include a predictionunit 1010, a subtraction unit 1020, a transformation unit 1030, aquantization unit 1040, an inverse quantization unit 1050, an inversetransformation unit 1060, an addition unit 1070, an in-loop filter unit1080, a memory unit 1090, and an encoding unit 1091. Some of the abovecomponents may not be necessarily included, and some or all of thecomponents may be selectively included in some implementations.

The prediction unit 1010 performs the prediction block generation stepS120 described with reference to FIG. 1 and generates a prediction blockto predict a pixel of a current block. That is, the various schemesdescribed in the prediction block generation step S120 of the intraprediction method according to the present invention described withreference to FIGS. 1, 2, 3A and 3B may be applied as a method by whichthe prediction unit 1010 performs the intra prediction.

The subtraction unit 1020 subtracts the prediction block from a encodingtarget block (i.e., a current block) to generate a residual block. Thatis, the subtraction unit 1020 calculates a difference between a pixelvalue of each pixel of the encoding target block and a prediction pixelvalue of each pixel of the prediction block predicted by the predictionunit 1010 to generate a residual block including a residual signal in ablock form.

The transformation unit 1030 transforms the residual block to afrequency domain and transforms each pixel value of the residual blockto a frequency coefficient. Here, the transformation unit 1030 maytransform the residual signal to the frequency domain using varioustransformation schemes of transforming a spatial axis image signal to afrequency axis, such as Hadamard transform or discrete cosine transformbased transform. The residual signal transformed to the frequency domainbecomes the frequency coefficient.

The quantization unit 1040 quantizes the residual block having thefrequency coefficient, which has been transformed to the frequencydomain by the transformation unit 1030. Here, the quantization unit 1040may quantize the transformed residual block using a dead zone uniformthreshold quantization (hereinafter referred to as DZUTQ), aquantization weighted matrix, an enhanced quantization scheme thereof,or the like.

The inverse quantization unit 1050 inversely quantizes the residualblock quantized by the quantization unit 1040. That is, the inversequantization unit 1050 inversely quantizes the quantization frequencycoefficients of the quantized residual block to generate a residualblock having a frequency coefficient.

The inverse transformation unit 1060 inversely transforms the residualblock inversely quantized by the inverse quantization unit 1050. Thatis, the inverse transformation unit 1060 inversely transforms thefrequency coefficients of the inversely quantized residual block togenerate a residual block having a pixel value, i.e., a restoredresidual block. Here, the inverse transformation unit 1060 may performinverse transformation by reversely using the transformation scheme usedin the transformation unit 1030.

The addition unit 1070 adds the prediction block predicted by theprediction unit 1010 to the residual block restored by the inversetransformation unit 1060 to restore the current block that is the targetblock.

The in-loop filter unit 1080 filters the current block restored by theaddition unit 1070. In this case, filtering is performed to reduce aquantization error or screen burn-in phenomenon between blocks. When theprediction unit 1010 performs the prediction by using the template or bysearching for the block most similar to the current block, as in theinter-frame prediction, in the intra prediction method, burn-in mayexist between blocks or the quantization error may be large in in thepreviously encoded region. In this case, when a template most similar tothe template from the adjacent block and the template in the previouslyencoded region is searched for, the similar template cannot be searchedfor or when the block most similar to the current block is searched for,the similar block cannot be searched for. Accordingly, the in-loopfiltering is applied when encoding ends in units of blocks.

Particularly, in the in-loop filter unit 1080 according to an embodimentof the present invention, the filtering coefficient value may becalculated based on a difference between an original pixel and arestored pixel, a certain coefficient value may be predefined and used,or the filtering coefficient value may be calculated based on therestored pixels.

Further, information on the difference between the original pixel andthe restored pixel may be sent in units of pixels, or pixels may begrouped according to a specific criterion and a representativedifference value of each group may be sent to the decoder. Particularly,the in-loop filter unit 1080 may perform existing filtering (forexample, de-blocking filtering) and filtering for correcting thedifference value due to the distortion between the original video andthe restored video, in combination. In this case, information onapplication of the filtering may be sent to the decoder in units ofsequences, pictures, slices, blocks or the like.

Accordingly, the encoder according to an embodiment of the presentinvention may perform encoding while changing whether to performfiltering, the number of filtering (the type of filtering), a filteringdirection and a filtering intensity based on the distortion between theoriginal video of the restored video obtained by summing the residualvideo and the prediction video and the restored video or based oncharacteristics of the restored video.

That is, in the encoder according to an embodiment of the presentinvention, an additional filter for improving image quality of anencoded frame may be applied. As the additional filter, an existingde-blocking filter may be used, as well as filtering may be performedusing a difference between the pixel of the original video and the pixelof the restored video due to the distortion between the original videoand the restored video, using a coefficient based on the difference, orbased on characteristics of the restored video. Thus, the additionalfilter may be applied independently from or together with thede-blocking filtering. Whether to apply the additional filter may bedetermined according to a size of the block or directivity of the block.

Accordingly, the in-loop filter unit 1080 according to an embodiment ofthe present invention may include at least one filter. A filter of thein-loop filter unit 1080 may include a de-blocking filter and at leastone additional filter.

Further, the in-loop filter unit 1080 may determine presence or absenceof a filtering to be applied, the number of filters, the type of filteror the like according to the size of the block or the directivity of theblock. Thus, it is possible to reduce the distortion between theoriginal video and the restored video as well as improve codingefficiency and subjective image quality. For example, when the size ofthe block is M×N and the directivity of the block is vertical as in FIG.6B, a filter such as [¼, ½, ¼] may be applied or when the directivity ofthe block is horizontal, the above filter may not be applied. Thus, thenumber of filters or the type of filter may be determined.

The memory unit 1090 stores the current block subjected to the in-loopfiltering so that the current block may be used as reference data when anext block of the current block or another block is encoded in future.

The encoding unit 1091 outputs a bit stream by encoding the quantizationfrequency coefficient string using an entropy coding scheme or the like.As this coding technology, entropy coding technology may be used but isnot limited thereto. Various coding technologies may be used.

Further, the encoding unit 1091 may include a bit string in whichquantization frequency coefficients have been encoded as well as variousinformation necessary to decode the encoded bit string, in the encodingdata. That is, the encoding data may include an encoded block pattern(CBP), a delta quantization parameter, a bit string in which thequantization frequency coefficient has been encoded, and a bit stringfor information necessary for prediction.

Configuration Example of Video Decoding Device in which Intra PredictionMethod According to the Present Invention has been Implemented

FIG. 11 is a block diagram for explaining a configuration example of avideo decoding device in which the intra prediction method according tothe present invention has been implemented.

Referring to FIG. 11, a video decoding device according to the presentinvention may include a decoding unit 1110, an inverse quantization unit1120, an inverse transformation unit 1130, a prediction mode decodingunit 1140, a prediction unit 1150, an addition unit 1160, an in-loopfilter unit 1170, and a memory unit 1180.

The decoding unit 1110 may decode and quantize a bit stream to extract aquantization frequency coefficient string, and inversely scan thequantization frequency coefficient to generate a residual block having aquantization frequency coefficient.

The inverse quantization unit 1120 and the inverse transformation unit1130 perform the same or similar functions as the inverse quantizationunit 1050 and the inverse transformation unit 1060 of the video encodingdevice described with reference to FIG. 10, respectively, andaccordingly a detailed description thereof will be omitted.

The prediction mode decoding unit 1140 decodes information on aprediction mode from the bit stream. When it is determined to be intraprediction in the prediction unit 1010 of a video encoding device,information on whether prediction has been performed using the firstmethod or the second method, which mode is used when the prediction hasbeen performed using the first method, and whether the prediction methodusing the template or the prediction method searching for a blocksimilar to a current block is used when the prediction has beenperformed using the second method is decoded. When the prediction isperformed using the template, the information on a, b, m, and ndescribed above is decoded, and when the prediction is performed bysearching for a block similar to the current block, information such asinformation on motion, information on a predictor of the motion isdecoded. Some of the information may not be necessarily included andsome or all of the information may be selectively included in someimplementations.

The prediction unit 1150 performs a similar role to the prediction unit1010 in the encoder and accordingly a detailed description thereof willbe omitted.

The addition unit 1160 adds a prediction block generated by theprediction unit 1150 to the residual block restored by the inversetransformation unit 1130 to restore a target block. The restored targetblock is filtered by the in-loop filter unit 1170 and then stored in thememory unit (1180) so that the target block can be used as referencedata when a next block of a current block or another block is restoredin future.

The in-loop filter unit 1170 plays a similar role to that in the encoderand accordingly a detailed description thereof will be omitted.

While the preferred embodiments of the present invention have beendescribed, it should be understood by those skilled in the art thatvarious changes and alterations may be made to the present inventionwithout departing from the spirit and scope of the invention defined bythe appended claims.

The invention claimed is:
 1. A video decoding method performed by avideo decoding apparatus, the method comprising: obtaining quantizedcoefficients of a current video by decoding an input bitstream;generating a residual video of the current video by performing aninverse-quantization and an inverse-transform on the quantizedcoefficients; generating a prediction video of the current video byusing an intra prediction mode relating to the current video andneighboring pixels adjacent to the current video; generating a restoredvideo by summing the residual video and the prediction video; andperforming in-loop filtering on the restored video, wherein theperforming the in-loop filtering comprises performing a deblockingfiltering; and performing, after the deblocking filtering, a secondaryfiltering, wherein the performing the secondary filtering comprisesdecoding information on a difference value from the input bitstream toobtain the difference value, the difference value being determined basedon a difference between a pixel of an original video and a correspondingpixel of the restored video and being obtained in a unit of a group ofpixels based on components comprising luminance and chrominance; andcorrecting the pixel of the restored video by adding the differencevalue to the pixel of the restored video.
 2. The method of claim 1,wherein the difference value is obtained respectively for a luminancecomponent and a chrominance component.
 3. A video decoding apparatuscomprising: a decoder configured to obtain quantized coefficients of acurrent video by decoding an input bitstream and generate a residualvideo of the current video by performing an inverse-quantization and aninverse-transform on the quantized coefficients; a predictor configuredto generate a prediction video of the current video by using an intraprediction mode relating to the current video and neighboring pixelsadjacent to the current video; an adder configured to generate arestored video by summing the residual video and the prediction video;and an in-loop filter configured to perform in-loop filtering on therestored video, wherein the performing the in-loop filtering comprisesperforming a deblocking filtering; and performing, after the deblockingfiltering, a secondary filtering, wherein the performing the secondaryfiltering comprises decoding information on a difference value from theinput bitstream to obtain the difference value, the difference valuebeing determined based on a difference between a pixel of an originalvideo and a corresponding pixel of the restored video and being obtainedin a unit of a group of pixels based on components comprising luminanceand chrominance; and correcting the pixel of the restored video byadding the difference value to the pixel of the restored video.
 4. Theapparatus of claim 3, wherein the difference value is obtainedrespectively for a luminance component and a chrominance component.
 5. Avideo encoding method performed by a video encoding apparatus, themethod comprising: obtaining quantized coefficients of a current video;generating a residual video of the current video by performing aninverse-quantization and an inverse-transform on the quantizedcoefficients; generating a prediction video of the current video byusing an intra prediction mode relating to the current video andneighboring pixels adjacent to the current video; generating a restoredvideo by summing the residual video and the prediction video; andperforming in loop filtering on the restored video, wherein theperforming the in-loop filtering comprises performing a deblockingfiltering; and performing, after the deblocking filtering, a secondaryfiltering, wherein performing the secondary filtering comprisesdetermining a difference value based on a difference between a pixel ofan original video and a corresponding pixel of the restored video, thedifference value being determined in a unit of a group of pixels basedon components comprising luminance and chrominance; correcting the pixelof the restored video by adding the difference value to the pixel of therestored video; and encoding information on the difference value into abitstream.
 6. A non-transitory computer-readable recording mediumstoring a bitstream that is generated by a video encoding methodperformed by a video encoding apparatus, the method comprising:obtaining quantized coefficients of a current video; generating aresidual video of the current video by performing aninverse-quantization and an inverse-transform on the quantizedcoefficients; generating a prediction video of the current video byusing an intra prediction mode relating to the current video andneighboring pixels adjacent to the current video; generating a restoredvideo by summing the residual video and the prediction video; andperforming in-loop filtering on the restored video, wherein theperforming the in-loop filtering comprises performing a deblockingfiltering; and performing, after the deblocking filtering, a secondaryfiltering, wherein performing the secondary filtering comprisesdetermining a difference value based on a difference between a pixel ofan original video and a corresponding pixel of the restored video, thedifference value being determined in a unit of a group of pixels basedon components comprising luminance and chrominance; correcting the pixelof the restored video by adding the difference value to the pixel of therestored video; and encoding information on the difference value into abitstream.